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At least 19 recordsLinked to original sources
PubMed1982

Acetylcholine concentration and its role in ionic transport by the corneal epithelium.

Corneal epithelium is known to have a high acetylcholine (ACh) concentration, but its role remains uncertain. Furthermore, rabbit corneal epithelium is devoid of cholinergic receptors. ACh concentration in calf, rabbit, and frog corneal epithelium was determined with Fellman's fluorometric assay to be 16.9, 11.1, and 21.8 micrograms of ACh per gram of epithelium, respectively. The isolated frog cornea was used to examine a possible role of the cholinergic system on active ionic transport. A 2 mM concentration of exogenous ACh has a moderate inhibitory effect on Na transport but no effect on Cl transport. A 10(-4)M concentration of 4-(1-naphthylvinyl) pyridine (NVP), a choline acetyltransferase inhibitor, reversibly inhibited both Na and Cl transport by about 70%. NVP also reduced ACh content of frog corneal epithelium by 51%. Thus endogenous ACh, but not exogenous ACh, seems to be stimulatory of active ionic transport. Of several muscarinic or nicotinic blockers tested, 10(-3)M atropine inhibited Na transport by 55% and Cl transport by 83%; 10(-3)M nicotine inhibited Na transport by 33% and Cl transport by 17%. If frog cornea (like rabbit cornea) contains no cholinergic receptors, the effects of ACh, nicotine, and atropine on ionic transport may be mediated through a nonspecific pathway.

Acetylcholine↗
PubMed1999

Identification of a cytosolic NADP+-dependent isocitrate dehydrogenase that is preferentially expressed in bovine corneal epithelium. A corneal epithelial crystallin.

Recently, metabolic enzymes have been observed in both the lens and corneal epithelium at levels greatly exceeding what is necessary for normal metabolic functions. These proteins have been termed taxon-specific crystallins and are thought to play a role in maintaining tissue transparency. We report here that cytosolic NADP+-dependent isocitrate dehydrogenase (ICDH) represents a new corneal crystallin. Using suppression subtractive hybridization, we identified a gene (with a deduced amino acid sequence that showed 94% identity to rat cytosolic NADP+-dependent ICDH) that is preferentially expressed in bovine corneal epithelium. Northern blots established that its mRNA level in the corneal epithelium was 31-, 39-, 133-, 230-, and 929-fold more than in the liver, bladder epithelium, stomach epithelium, brain, and heart, respectively. This mRNA was detected primarily in corneal epithelial basal cells by in situ hybridization. SDS-polyacrylamide gel electrophoresis, two-dimensional gel analysis, and Western blotting showed that this protein was overexpressed in the corneal epithelium, constituting approximately 13% of the total soluble bovine corneal epithelial proteins. Enzyme assays showed a corresponding overabundance of this protein in bovine corneal epithelium. Taken together, these data indicate that bovine cytosolic ICDH fulfills the criteria for a corneal epithelial crystallin and may be involved in maintaining corneal epithelial transparency.

Amino Acid Sequence↗
PubMed2000

The effects of the topical administration of non-steroidal anti-inflammatory drugs on corneal epithelium and corneal sensitivity in normal subjects.

PURPOSE: To study the changes in the corneal epithelium and corneal sensitivity of healthy subjects after the topical administration of non-steroidal anti-inflammatory drugs (NSAIDs; diclofenac, indomethacin, flurbiprofen and ketorolac) frequently used in ocular therapy. METHODS: A double-masked parallel clinical study was undertaken on 90 subjects (45 men, 45 women; Caucasian; age 21-46 years, mean +/- SD 27.1 +/- 5 years). The subjects were divided into six groups: group 1 was treated with placebo, group 2 with 0.1% diclofenac, group 3 with 0.1% indomethacin, group 4 with 0.03% flurbiprofen, group 5 with 0.5% ketorolac and group 6 with 0.4% oxybuprocaine. One eye was randomly treated with the study drug and the fellow eye was treated with placebo. The medications were instilled four times, at 5 min intervals. Assessment of the corneal epithelium was carried out by vital fluorescein stain before instillation and 5, 15, 30 and 60 min after instillation of the last drop. Subjective burning sensation was assessed by asking participants to rate burning on a scale from 0 (none) to 3 (severe). After 1 week, assessment of corneal sensitivity was carried out by the Cochet-Bonnet method, repeating the above scheme of instillation and measurement times. RESULTS: None of the study drugs, with the exception of oxybuprocaine, produced evident epithelial damage. All the drugs caused a mean burning sensation greater than the placebo. The diclofenac-treated group showed a statistically significant decrease in corneal sensitivity (p < 0.001) at the measurement carried out 15 min after instillation of the last drop and lasting up to the end of the study, when the corneal anaesthesia was similar to that induced by the topical anaesthetic treatment. No significant changes were demonstrated for the other NSAIDs when compared either with the placebo-treated eyes or with the fellow eyes. CONCLUSIONS: Despite a similar mechanism of action and analgesic activity to the other NSAIDs tested, diclofenac was able to induce a reduction in corneal sensitivity. More studies are needed to determine the mechanism of action responsible for this effect.

Adult↗
PubMed2004

What does overnight lens wear do to the corneal epithelium?: is corneal refractive therapy different?

The corneal epithelium plays a central role in preventing infectious keratitis. It is a layer that functions both as a physical barrier and as an active component of the ocular surface defense system. Contact lens wear is capable of altering the structure and physiology of the corneal epithelium, potentially increasing the risk of infectious keratitis. This brief review summarizes the effects of continuous contact lens wear and corneal refractive therapy on the physiology and structure of the corneal epithelium.

Animals↗
PubMed1987

Co-culture of rat trigeminal ganglion neurons and corneal epithelium.

Corneal epithelium and the trigeminal ganglion neurons which normally innervate the epithelium have been grown in adjacent chambers of a 35 mm tissue culture plate. Dissociated nerve cells from late embryonic rats were plated inside an 8 mm cloning cylinder attached to the center of the culture plate by silicone grease. In 7-10 days neurites extended out of this inner chamber by growing through the grease seal and along parallel scratches in the collagen coating of the tissue culture plate. Once this occurred, pure corneal epithelial explants were isolated from young adult rats and plated in the area surrounding the cloning cylinder, i.e. in the outer chamber. Cultures were monitored regularly with phase microscopy and, at various times, were fixed for ultrastructural examination. Within 24-48 hours of the epithelial plating, there were both individual neurites and bundles of neurites in contact with the epithelium. This interaction increased substantially over the next few days. Growth cones of the neurites could be seen to approach the microvilli-covered surface of the epithelium, travel over the surface and penetrate between the epithelial cells. This tissue culture model of the innervated ocular surface may prove valuable in the study of a variety of ocular conditions or diseases, as well as provide a means to study functional relationships and mechanisms of cellular interaction between neurons and their target cells.

Animals↗
PubMed1975

Transmissible mink encephalopathy: infectivity of corneal epithelium.

Corneal epithelium from hamsters dying of transmissible mink encephalopathy contained a virus titer of 10-4.8 times the 50 percent lethal dose (10-4.8 LD50) per 0.05 milliliter when assayed as a cell suspension derived directly from the infected animal. After one passage in tissue culture, an equivalent concentration of cells contained only 10-0.8 LD50 per 0.05 milliliter.. It is concluded that corneal tissues are infectious; the infectivity may be mainly associated with free nerve endings. However, the most important immediate inference is that corneas from human beings affected with Creuzfeldt-Jakob disease are likely to be lethal if transplanted to healthy recipients.

Animals↗
PubMed2000

Changes of cytochemical markers in the conjunctival and corneal epithelium after corneal debridement.

1. The aim of this study was to determine the epithelial changes of the conjunctiva and cornea up to 7 days after corneal debridement and the changes highlighted included (1) proliferation, (2) production of growth factor, (3) changes in calcium binding protein marker, (4) production of cytokine, and (5) maturity of the regeneration corneal epithelium. 2. The cytochemical changes of the corneal and conjunctival epithelia of rabbit were analyzed up to 7 days after debridement. 3. An increase in proliferating cell nuclear antigen (PCNA) was observed in the limbal epithelia 12 hr after lesion and reached a peak by 48 hr. 4. Some proliferating limbal cells also contained epidermal growth factor (EGF) beginning 24 hr after injury. The early limbal cell proliferation and the EGF production and their persistence until 7 days after lesion were likely involved with the process of regeneration. 5. Other positive markers appeared after lesion included tumor necrosis factor (TNFalpha) and calcium binding proteins S100A and S100B, which appeared mainly within the first 48 hr after lesion and then started to decline. The short appearance and the relatively small quantity of TNFalpha indicated that this cytokine was probably not very important in the repair process and its appearance might be related to the injury induced. The presence of S100A and S100B could be associated with both cell death after injury and the proliferation of new epithelium. 6. The cornea epithelium was still immature 7 days after lesion in that it still contained cytokeratin. 7. In conclusion, the critical hours of peak conjunctival and corneal changes after corneal debridement were in the first 2 days.

Animals↗
PubMed1990

Calpain and calpastatin in rabbit corneal epithelium.

The purpose of this study was to provide a direct assay for calpain and its endogenous inhibitor calpastatin in normal rabbit epithelium. Corneal epithelial extracts were fractionated by DEAE (1) chromatography on HPLC. Fractions were analyzed for calpain by ELISA, immunoblotting, and caseinolytic enzyme activity with FITC-labeled casein. Results demonstrated immunoreactive peaks for calpains I and II. Calpain II from the soluble fraction of corneal epithelium eluted at a similar NaCl concentration (260 mM) as calpain II from other tissues, was inhibited by both E64 and the removal of Ca, contained an 80 kDa subunit in immunoblots, and was present at specific activity of 220 units/g protein (in a crude homogenate). Calpain antigen was also present in the EDTA/EGTA washed insoluble fraction of corneal epithelium. Calpastatin in corneal epithelium eluted at 130 - 160 mM NaCl on DEAE, coeluted with calpain I, and was present at 330 units/g protein (crude homogenate). The results demonstrated a calpain/calpastatin system in corneal epithelium, where it is speculated to play a role in epithelial cell turnover and wound healing.

Animals↗
PubMed1986

Ultrastructure of conjunctival epithelium replacing corneal epithelium.

After corneas of mice had been totally denuded of their epithelium by the application of n-heptanol, the new epithelium which grew over the corneas was studied by electron microscopy at intervals up to 7 months. The purpose was to compare the basal attachment of the new cells, derived from conjunctiva, with that of true corneal epithelial cells growing on the same type of substratum, and studied previously. Goblet cells appeared after 2 weeks amid the squamous type of epithelial cells which had resurfaced the cornea in about 1 week. Goblet cells increased up to at least 6 weeks, but had decreased by 3 months. They persisted, however, for the entire 7 months of the study. Goblet cells had only a small area of contact with the basal lamina, and they had few desmosomes or hemidesmosomes. Basal cells of the squamous type had complex features of their basal attachment quite different from those of normal or repairing corneal epithelial cells studied previously. Flat cytoplasmic extensions of squamous cells underlay most of the goblet cell basal pole which therefore had only a small area on the basal lamina. Numerous filaments inserted into desmosomes and hemidesmosomes of squamous cells, and prominent bundles of these filaments lay just above the basal plasma membrane. They were orientated parallel to the radial axis of the cornea. Closely spaced corrugations of the basal plasma membrane were also orientated in this axis, as well as rows of hemidesmosomes. Even after a period of 7 months, the morphological features of conjunctival cells did not come to resemble those of normal corneal epithelium. The radial arrangement of fibers, hemidesmosome rows, and corrugations is interpreted as a reflection of the continued centripetal migration of the epithelium.

Animals↗
PubMed1985

A noninvasive optical method to measure oxygen tension at the corneal epithelium.

Corneal redox fluorometry is presented as an alternative method to noninvasively measure the oxygen tension in equilibrium with the tear film. The application of this method to the study of the effects of a contact lens on the tear film oxygen tension is described. The development of a clinical corneal redox fluorometer would permit noninvasive measurements of the effects of contact lens induced corneal hypoxia on corneal physiology. These studies could investigate the effects of corneal hypoxia at the cellular level and result in a new level of understanding of the processes involved.

Animals↗
PubMed1997

Gefarnate stimulates secretion of mucin-like glycoproteins by corneal epithelium in vitro and protects corneal epithelium from desiccation in vivo.

The effect of drugs for gastritis and gastric ulcer (ecabet sodium, gefarnate, teprenone, and troxipide) on the secretion of mucin-like glycoproteins from rat cornea were investigated in vitro and on a short-term, rabbit dry eye model in vivo. For the studies in vitro, cultured rat cornea sections (3 mm diameter) were incubated with radiolabeled sodium sulfate, rinsed, and then incubated for 30 min in the presence of one of the drugs. The culture media were reacted with Dolichos biflorus agglutinate (DBA)-lectin, and the radioactivity of DBA-bound mucin-like glycoproteins was measured. A cytotoxicity assay confirmed that mucin-like glycoproteins had not leaked from damaged cells. For studies in vivo, eye drop vehicle or drops containing gefarnate were instilled in the eyes of nine anesthetized rabbits, and then the eyes were kept open with specula for two hours. These rabbits and two control rabbits not subjected to ocular drying were killed, and their eyes were enucleated and stained with methylene blue. Corneal epithelial damage from desiccation was evaluated based on the extent of methylene blue staining. Among the four kinds of drugs for gastritis and gastric ulcers, only gefarnate significantly increased the mucin-like glycoprotein secretion from cultured rat corneas in vitro; this stimulatory effect of gefarnate was dose-dependent. In vivo, the instillation of gefarnate reduced corneal epithelial damage from desiccation in a dose-dependent fashion. These results suggest that gefarnate reduces desiccation of corneal epithelium, perhaps by stimulating secretion of mucin-like glycoproteins from corneal epithelium.

Animals↗
PubMed1988

Double vital staining of corneal epithelium after corneal transplantation with a rose bengal-fluorescein mixture.

Longitudinal double vital staining with 1% rose bengal (RB) and 1% fluorescein (Flu) has been carried out on 33 eyes subjected to penetrating corneal transplantation. At the conclusion of the operation pronounced desiccation of both donor's and recipient's epithelium was seen in a scant 50%, but abrasion in only 8%. the desiccation subsided during the first post-operative day, but the donor's epithelium was rejected in the majority (91%). Healing started on the third day, manifesting itself by Flu-punctate whorl-shaped epithelium invading or gliding across the wound. By the fifth day nearly complete healing had occurred. In 9% no renewal of epithelium was noticed. Subsequent control examinations revealed loose sutures (RB-stained mucous adhesions), evanescent cicatricial defects, and open suture canals (Flu). Graft rejection occurred in 8 cases. In 5 of these, well-defined massive peripheral staining of donor epithelium was seen (RB most widespread and sharply outlined), and in the remaining 3, uncharacteristic, diffuse, punctate staining.

Cornea↗
PubMed1986

Autoimmunity against corneal antigens. I. Isolation of a soluble 54 Kd corneal epithelium antigen.

Corneal epithelium antibodies were detected in patients with corneal melting disease and uveitis using an immunofluorescence technique with cryostat sections of corneas obtained from various species (man, guinea pig, rabbit, mouse, rat, cow, pig). No differences in results were found using these various substrates, indicating that the autoimmune response is directed against common non-species specific corneal epithelium antigens. The serum of a patient with corneal melting disease, containing a high antibody titer against corneal epithelium was used to identify and isolate one of the bovine corneal antigens. A 54,000 dalton protein was isolated, which was shown to be the major protein present in the corneal epithelium. Absorption studies with other tissues taken from human eyes showed that cornea epithelium, cornea devoid of epithelium, ciliary body and retina contained material which cross-reacted with the isolated bovine corneal epithelium antigen, whereas iris and sclera showed no detectable cross-reaction. The incidence of autoantibodies directed against this antigen was investigated in patients with corneal melting disease, corneal transplantion and in uveitis patients using an ELISA and comparing the results with those obtained with the immunofluorescence assay on rabbit cornea sections. A positive ELISA was always associated with a positive immunofluorescence test. The presence of antibodies against the 54 Kd antigen as detected by the ELISA could be confirmed by immunoblotting in 7 out of 9 positive sera tested. A large number of sera showed a positive immunofluorescence test but a negative ELISA against the 54 Kd corneal epithelium antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1986

Clinical and experimental studies concerning circulating antibodies to corneal epithelium antigens.

Corneal epithelium antibodies were detected in patients with corneal melting disease (55%), uveitis (42%), corneal transplantation (42%) and marginal furrow disease (20%). These antibodies were not found in herpetic keratitis patients. In control groups, consisting of ocular surgery patients (glaucoma, retinal detachment and cataract) and persons without a history of ocular disease, approximately 4% of the subjects had these antibodies. To investigate the possible role of trauma to the cornea as an initiator of corneal epithelium antibodies, these antibodies were determined in rabbits after alkaline burns were made on the cornea. These antibodies were detected one week later and disappeared after six weeks. Serum from three patients with corneal melting disease and corneal transplantation containing a high antibody titre against corneal epithelium were used to isolate corneal epithelium antigens. A 54 kD and a 17 kD corneal epithelium antigen were isolated. The incidence of autoantibodies directed against these antigens was investigated in patients with corneal melting disease, uveitis and corneal transplantation using an ELISA. 50% of the sera positive in the immunofluorescence test were positive in the ELISA.

Adult↗
PubMed1998

Reactive oxygen species (ROS) generated by xanthine oxidase in the corneal epithelium and their potential participation in the damage of the corneal epithelium after prolonged use of contact lenses in rabbits.

Prolonged use of contact lenses (for 14 days) evoked an imbalance between the activity of xanthine oxidase (an enzyme belonging to reactive oxygen species-generating oxidases) and catalase (an enzyme belonging to reactive oxygen species-scavenging oxidases) in the corneal epithelium of rabbits. The activity of catalase decreased, while xanthine oxidase activity was very high. Of other enzymes studied in the corneal epithelium, the activities of xanthine oxidoreductase, glucoso-6-phosphate dehydrogenase and succinate dehydrogenase were decreased. In contrast, the activities of lactate dehydrogenase and lysosomal hydrolases (acid beta-galactosidase, dipeptidyl peptidase II) were increased and appeared in animals sacrificed immediately after contact lens removal. In rabbits sacrificed later (after 1 h), an additional increase of lactate dehydrogenase and lysosomal hydrolase activities developed in the superficial layers of the corneal epithelium. Catalase supplementation during use of contact lenses prevented both the significant decrease of catalase activity in the corneal epithelium and the development of additional epithelial damage. In contrast, topical treatment with 3-aminotriazole (an inhibitor of catalase) resulted in the nearly complete loss of catalase activity in the corneal epithelium and the appearance of more serious epithelial damage. We conclude that ROS generated by xanthine oxidase induce additional damage of the corneal epithelium related to the use of contact lenses.

Animals↗
PubMed1999

cDNA cloning of 15-lipoxygenase type 2 and 12-lipoxygenases of bovine corneal epithelium.

Bovine corneal epithelium contains arachidonate 12- and 15-lipoxygenase activity, while human corneal epithelium contains only 15-lipoxygenase activity. Our purpose was to identify the corneal 12- and 15-lipoxygenase isozymes. We used cDNA cloning to isolate the amino acid coding nucleotide sequences of two bovine lipoxygenases. The translated sequence of one lipoxygenase was 82% identical with human 15-lipoxygenase type 2 and 75% identical with mouse 8-lipoxygenase, whereas the other translated nucleotide sequence was 87% identical with human 12-lipoxygenase of the platelet type. Expression of 15-lipoxygenase type 2 and platelet type 12-lipoxygenase mRNAs were detected by Northern analysis. In addition to these two lipoxygenases, 12-lipoxygenase of leukocyte (tracheal) type was detected by polymerase chain reaction (PCR), sequencing, and Northern analysis. Finally, PCR and sequencing suggested that human corneal epithelium contains 15-lipoxygenase types 1 and 2.

Amino Acid Sequence↗
PubMed1994

Arachidonate 15-lipoxygenase in human corneal epithelium and 12- and 15-lipoxygenases in bovine corneal epithelium: comparison with other bovine 12-lipoxygenases.

Lipoxygenases of bovine and human corneal epithelia were investigated. The bovine epithelium contained an arachidonate 12-lipoxygenase and a 15-lipoxygenase. The 12-lipoxygenase was found in the microsomal fraction, while the 15-lipoxygenase was mainly present in the cytosol (100,000 x g supernatant). 12S-Hydroxyeicosatetraenoic acid (12S-HETE) and 15S-hydroxyeicosatetraenoic acid (15S-HETE) were identified by GC-MS and chiral HPLC. BW A4C, an acetohydroxamic acid lipoxygenase inhibitor, reduced the biosynthesis of 12S-HETE and 15S-HETE by over 90% at 10 microM. IC50 for the 12-lipoxygenase was 0.3 microM. The bovine corneal 12-lipoxygenase was compared with the 12-lipoxygenases of bovine platelets and leukocytes. All three enzymes metabolized 14C-labelled linoleic acid and alpha-linolenic acid poorly (5-16%) in comparison with [14C]arachidonic acid. [14C]Docosahexaenoic acid and [14C]4,7,10,13,16-docosapentaenoic acid appeared to be less efficiently converted by the corneal enzyme than by the platelet and leukocyte enzymes. Immunohistochemical analysis of the bovine corneal epithelium using a polyclonal antibody against porcine leukocyte 12-lipoxygenase gave positive staining. The cytosol of human corneal epithelium converted [14C]arachidonic acid to one prominent metabolite. The product co-chromatographed with 15S-HETE on reverse phase HPLC, straight phase HPLC and chiral HPLC. Our results suggest that human corneal epithelium contains a 15-lipoxygenase and that bovine corneal epithelium contains both a 15-lipoxygenase and a 12-lipoxygenase. The corneal 12-lipoxygenase appears to differ catalytically from earlier described bovine 12-lipoxygenases.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗